Methods and compositions for treating pain

ABSTRACT

The disclosure provides a new use of adenosine analogs for the treatment of pain through activation of neurokinin 1 (NK1) receptor signaling pathway, thereby inducing the activation of M-type potassium channel to induce outward currents. A method and pharmaceutical composition for treating pain comprising an adenonsine analog that activates NK1 receptor signaling, thereby inducing outward current are also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. provisional application underSer. No. 61/597,742, filed on Feb. 11, 2012, and herein incorporated byreference in its entirety.

BACKGROUND OF THE INVENTION

The present invention is directed to medical methods and compositionsfor treatment of pain, in particularly acid-induced pain.

Pain is an unpleasant sensory and emotional experience associated withactual or potential tissue damage, for example, which may result fromdamage to body tissue, for example in general medical illnesses, cancer,neuropathies, and perioperative conditions. Pain may also be associatedwith medical disorders without a known cause, such as migraine andpsychosomatic illness.

It is known Substance P (SP) is an undecapeptide belonging to thetachykinin small peptide family. SP is a pain neurotransmitter thathelps excite and transmit pain signals from neural cells in many organs.Substance P is an important element in pain perception. The sensoryfunction of substance P is thought to be related to the transmission ofpain information into the central nervous system. Substance P coexistswith the excitatory neurotransmitter glutamate in primary afferents thatrespond to painful stimulation. (De Felipe et al., Altered nociception,analgesia and aggression in mice lacking the receptor for substance P.Nature 392 (6674): 394-397, March 1998.) High levels of SP in muscletissues and spinal fluid are frequently associated with chronic musclepain such as myofascial pain syndrome and fibromyalgia, but the role ofSP in muscle pain transmission and perception was unclear.

It was disclosed by Lin et al. that SP is an antinociceptive role inacid-induced chronic muscle pain. Lin showed that a single i.m. acidinjection in mice lacking SP signaling by deletion of the tachykininprecursor 1 (Tac1) gene or coadministration of NK1 receptor antagonistsproduced long-lasting hyperalgesia rather than the transienthyperalgesia seen in control animals, and the inhibitory effect of SPwas found exclusively in neurons expressing acid-sensing ion channel 3,where SP enhanced M-channel-like potassium currents through the NK1receptor in a G protein-independent but tyrosine kinase-dependentmanner. Furthermore, the SP signaling could alter action potentialthresholds and modulate the expression of TTX-resistant sodium currentsin medium-sized muscle mociceptor. (Lin et al., An antinociceptive rolefor substabce P in acid-induced chronic muscle pain. PNAS 109 (2):E76-E83, January 2012.)

It is still desirable to develop a method or pharmaceutical compositionfor treating or managing pain.

SUMMARY OF THE INVENTION

The present invention is based on the unexpected discovery that a numberof adenosine analogs are effective for the treatment of pain throughactivation of neurokinin 1 (NK1) receptor signaling pathway in musclenociceptors, thereby inducing the activation of activation of M-typepotassium channel to induce outward currents.

In one aspect, the present invention provides a use in the manufactureof a medicament for treating pain of an adenonsine analog that activatesNK1 receptor signaling, thereby inducing outward current.

In certain embodiments of the invention, the pain is an acid-inducedpain. In an example, the pain is an acid-induced muscle pain,particularly an acid-induced chronic muscle pain.

According to the invention, the pain may also be selected from the groupconsisting of inflammatory pain, cancer pain, chest pain, back pain,facial pain, joint pain, muscular pain syndromes, neuropathic pain,peripheral pain, cancer and tumor pain, sympathetic pain, postoperativepain, and post-traumatic pain.

In some certain examples of the invention, the pain may also befibromyalgia, myofascial pain, bladder pain syndrome or pain casued byirritable bowel syndrome.

In one example of the invention, the adenosine analog is isolated from aGastrodia extract.

In certain embodiments of the invention, the adenosine analog is acompound of Formula (I):

or a pharmaceutically acceptable salt thereof,wherein:

X is 0, S or CH₂;

R¹ is selected from the group consisting of NHR⁴, NH(CH₂)_(n)R⁴,NH—NHR⁴, NHCONHR⁴, NH—OR⁴, O—NHR⁴, and SR⁴;

R² is selected from the group consisting of hydrogen (H), halogen,cyano, OR⁴, NHR⁴, substituted or unsubstituted alkyl, substituted orunsubstituted alkenyl, substituted or unsubstituted alkynyl, substitutedor unsubstituted cycloalkyl, substituted or unsubstituted aryl (Ar),substituted or unsubstituted aralkyl, and a substituted or unsubstitutedheterocyclyl;

R³ is selected from the group consisting of halomethyl, hydroxymethyl(HOCH₂), alkoxymethyl (R⁴OCH₂), azidomethyl (N₃CH₂), aminomethyl(H₂NCH₂), substituted or unsubstituted aminomethyl, amidomethyl(H₂NCOCH₂), sulfanylmethyl (R⁴S), sulfonylmethyl (R⁴SO₂),triazolylmethyl, cyanomethyl (N≡CCH₂), cyano, substituted orunsubstituted carbonyl (R⁴CO), COOH, substituted or unsubstitutedaminocarbonyl (R⁴HNCO), substituted or unsubstituted alkynyl, andsubstituted or unsubstituted tetrazole;

n is 1, 2 or 3;

each instance of R⁴ is independently selected from the group consistingof H, alkyl, cycloalkyl, substituted or unsubstituted Ar, substituted orunsubstituted aralkyl, and a substituted or unsubstituted heterocyclyl;

Ar is selected from the group consisting of substituted or unsubstitutedphenyl, substituted or unsubstituted polyarene, and a substituted orunsubstituted heterocycle.

In some certain embodiments of the present invention, the adenosineanalog is a compound of Formula (II):

or a pharmaceutically acceptable salt thereof.

In one example of the compound of formula (II) according to theinvention, the adenosine analog is N⁶-(4-hydroxybenzyl)adenosine havingthe formula T1-11:

or a pharmaceutically acceptable salt thereof.

In another example of the compound of formula (II) according to theinvention, the adenosine analog is a compound having the formulaJMF1998:

or a pharmaceutically acceptable salt thereof.

In a further example of the compound of formula (II) according to theinvention, the adenosine analog is a compound having the formulaJMF2665:

or a pharmaceutically acceptable salt thereof.

In other embodiments of the present invention, the adenosine analog is acompound of formula (III):

or a pharmaceutically acceptable salt thereof, wherein Het is asubstituted or unsubstituted heterocycle comprising 5- or 6-memberedring or fused ring containing at least one nitrogen, oxygen or sulfurheteroatoms.

In preferred embodiments of the invention, Het is selected from thegroup consisting of pyrrole, furan, thiophene, pyridine, piperidine,piperazine, indole, benzofuran, benzothiophene, and quinoline.

In one example of the compound of formula (III) according to theinvention, the adenosine analog is a compound having the formulaJMF1907:

or a pharmaceutically acceptable salt thereof.

In further embodiments of the invention, the adenosine analog is acompound of formula (IV):

or a pharmaceutically acceptable salt thereof.

In one preferred example of the compound of formula (IV) according tothe invention, the adenosine analog is a compound having the formulaCGS21680:

or a pharmaceutically acceptable salt thereof.

In some embodiments, the adenosine analog according to the presentdisclosure can be selected from the following:

In another aspect, the present invention provides a pharmaceuticalcomposition of use for treating pain (e.g., those described herein)comprising an effective amount of an andenosine analog as defined above,and a pharmaceutically acceptable carrier.

In further aspect, the present invention provides a method of treatingpain, comprising administering to a subject in need thereof an effectiveamount of the andenosine analog as described herein, or a pharmaceuticalcomposition comprising the andenosine analog as defined above.

DEFINITIONS

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention pertains. In the case of conflict, thepresent document, including definitions will control.

As used herein, the singular forms “a”, “an”, and “the” include pluralreferents unless the context clearly dictates otherwise. Thus, forexample, reference to “a sample” includes a plurality of such samplesand equivalents thereof known to those skilled in the art.

As used herein, the term “subject” refers to a human or a mammal, suchas a patient, a companion animal (e.g., dog, cat, and the like), a farmanimal (e.g., cow, sheep, pig, horse, and the like) or a laboratoryanimal (e.g., rat, mouse, guinea pig, and the like).

As used herein, the terms “treatment,” “treating,” and the like, referto obtaining a desired pharmacologic and/or physiologic effect. Theeffect may be prophylactic in terms of completely or partiallypreventing a disease or condition, or symptom thereof, and/or may betherapeutic in terms of a partial or complete cure for a conditionand/or adverse affect attributable to the condition. The term“treatment” as used herein, covers any treatment of a disease orcondition in a mammal, particularly in a human, and includes: (a)preventing the condition from occurring in a subject which may bepredisposed to the condition but has not yet been diagnosed as havingit; (b) inhibiting the development of the condition; and/or (c)relieving the condition, i.e., causing its regression.

As used herein, the phrase “an effective amount” refers to an amountsufficient to effect beneficial or desired results. An effective amountcan be administered in one or more administrations. An effective amountcorresponds with the quantity required to provide a desired averagelocal concentration of a particular biologic agent, in accordance withits known efficacy, for the intended period of therapy. A dose may bedetermined by those skilled in the art by conducting preliminary animalstudies and generating a dose response curve, as is known in the art.Maximum concentration in the dose response curve would be determined bythe solubility of the compound in the solution and by toxicity to theanimal model, as known in the art. The effective amount furthercorresponds with the quantity required to provide a desired averagelocal concentration of the particular biologic agent, in accordance withits efficacy for the intended period of time. Due allowance can be madefor losses due to circulatory fluctuation due to physical activity, forexample, from ten to ninety percent loss allowance could be madedepending upon the individual patient and their routines.

The term “pain” as used herein refers to an unpleasant feeling oftencaused by intense or damaging stimuli, including different types andsymptoms of pain, either acute or chronic pain, especially inflammatorypain, cancer pain, chest pain, back pain, facial pain, joint pain,muscular pain syndromes, neuropathic pain, peripheral pain, cancer andtumor pain, sympathetic pain, postoperative pain, and post-traumaticpain.

Definitions of specific functional groups and chemical terms aredescribed in more detail below. For purposes of this invention, thechemical elements are identified in accordance with the Periodic Tableof the Elements, CAS version, Handbook of Chemistry and Physics, 75thEd., inside cover, and specific functional groups are generally definedas described therein. Additionally, general principles of organicchemistry, as well as specific functional moieties and reactivity, aredescribed in “Organic Chemistry,” Thomas Sorrell, University ScienceBooks, Sausalito: 1999, the entire contents of which are incorporatedherein by reference for the purposes or subject matter referencedherein.

As used herein, the term “alkyl” is given its ordinary meaning in theart and refers to the radical of saturated aliphatic groups, includingstraight-chain alkyl groups, branched-chain alkyl groups, cycloalkyl(alicyclic) groups, alkyl substituted cycloalkyl groups, and cycloalkylsubstituted alkyl groups. In some cases, the alkyl group may be a loweralkyl group, i.e., an alkyl group having 1 to 10 carbon atoms (e.g.,methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, ordecyl). In some embodiments, a straight chain or branched chain alkylmay have 30 or fewer carbon atoms in its backbone, and, in some cases,20 or fewer. In some embodiments, a straight chain or branched chainalkyl may have 12 or fewer carbon atoms in its backbone (e.g., C₁-C₁₂for straight chain, C₃-C₁₂ for branched chain), 6 or fewer, or 4 orfewer. Likewise, cycloalkyls may have from 3-10 carbon atoms in theirring structure, or 5, 6 or 7 carbons in the ring structure. Examples ofalkyl groups include, but are not limited to, methyl, ethyl, propyl,isopropyl, cyclopropyl, butyl, isobutyl, t-butyl, cyclobutyl, hexyl, andcyclochexyl.

The terms “alkenyl” and “alkynyl” are given their ordinary meaning inthe art and refer to unsaturated aliphatic groups analogous in lengthand possible substitution to the alkyls described above, but thatcontain at least one double or triple bond respectively.

The term “cycloalkyl,” as used herein, refers specifically to groupshaving three to ten, preferably three to seven carbon atoms. Suitablecycloalkyls include, but are not limited to cyclopropyl, cyclobutyl,cyclopentyl, cyclohexyl, cycloheptyl and the like, which, as in the caseof other aliphatic, heteroaliphatic, or hetercyclic moieties, mayoptionally be substituted with substituents including, but not limitedto aliphatic; heteroaliphatic; aryl; heteroaryl; arylalkyl;heteroarylalkyl; alkoxy; aryloxy; heteroalkoxy; heteroaryloxy;alkylthio; arylthio; heteroalkylthio; heteroarylthio; —F; —Cl; —Br; —I;—OH; —NO₂; —CN; —CF₃; —CH₂CF₃; —CHCl₂; —CH₂OH; —CH₂CH₂OH; —CH₂NH₂;—CH₂SO₂CH₃; —C(O)R_(x); —CO₂(R_(x)); —CON(R_(x))₂; —OC(O)R_(x);—OCO₂R_(x); —OCON(R_(x))₂; —N(R_(x))₂; —S(O)₂R_(x); —NR_(x)(CO)R_(x),wherein each occurrence of R_(x) independently includes, but is notlimited to, aliphatic, heteroaliphatic, aryl, heteroaryl, arylalkyl, orheteroarylalkyl, wherein any of the aliphatic, heteroaliphatic,arylalkyl, or heteroarylalkyl substituents described above and hereinmay be substituted or unsubstituted, branched or unbranched, cyclic oracyclic, and wherein any of the aryl or heteroaryl substituentsdescribed above and herein may be substituted or unsubstituted.Additional examples of generally applicable substitutents areillustrated by the specific embodiments shown in the Examples that aredescribed herein.

The term “aryl” or “Ar” as used herein is given its ordinary meaning inthe art and refers to aromatic carbocyclic groups, substituted orunsubstituted, having a single ring (e.g., phenyl), or multiple fusedrings, including phenyl, polyarene, and heterocycle comprising 5- or6-membered ring or fused ring containing at least one nitrogen, oxygenor sulfur heteroatoms. Substituents include, but are not limited to thesubstituents recited for aliphatic moieties, or for other moieties asdisclosed herein, resulting in the formation of a stable compound. Insome cases, the heterocycle may be 3- to 10-membered ring structures or3- to 7-membered rings, whose ring structures include one to fourheteroatoms.

Heterocycles include, for example, thiophene, benzothiophene,thianthrene, furan, tetrahydrofuran, pyran, isobenzofuran, chromene,xanthene, phenoxathiin, pyrrole, dihydropyrrole, pyrrolidine, imidazole,pyrazole, pyrazine, isothiazole, isoxazole, pyridine, pyrazine,pyrimidine, pyridazine, indolizine, isoindole, indole, indazole, purine,quinolizine, isoquinoline, quinoline, phthalazine, naphthyridine,quinoxaline, quinazoline, cinnoline, pteridine, carbazole, carboline,triazole, tetrazole, oxazole, isoxazole, thiazole, isothiazole,phenanthridine, acridine, pyrimidine, phenanthroline, phenazine,phenarsazine, phenothiazine, furazan, phenoxazine, pyrrolidine, oxolane,thiolane, oxazole, oxazine, piperidine, homopiperidine(hexamnethyleneimine), piperazine (e.g., N-methyl piperazine),morpholine, lactones, lactams such as azetidinones and pyrrolidinones,sultams, sultones, other saturated and/or unsaturated derivativesthereof, and the like. The heterocyclic ring can be optionallysubstituted at one or more positions with such substituents as describedherein. In some cases, the heterocycle may be bonded to a compound via aheteroatom ring atom (e.g., nitrogen). In some cases, the heterocyclemay be bonded to a compound via a carbon ring atom. In some cases, theheterocycle is pyridine, imidazole, pyrazine, pyrimidine, pyridazine,acridine, acridin-9-amine, bipyridine, naphthyridine, quinoline,benzoquinoline, benzoisoquinoline, phenanthridine-1,9-diamine, or thelike.

All of the compounds described above may be in a variety of forms,including the compounds themselves, as well as their pharmaceuticallyacceptable salts, salvates, and hydrates, etc.

The term “pharmaceutically acceptable salt” as used herein refers tothose salts which are, within the scope of sound medical judgment,suitable for use in contact with the tissues of humans and lower animalswithout undue toxicity, irritation, allergic response and the like, andare commensurate with a reasonable benefit/risk ratio. Pharmaceuticallyacceptable salts are well known in the art. For example, Berge et al.,describe pharmaceutically acceptable salts in detail in J.Pharmaceutical Sciences, 1977, 66, 1-19, incorporated by referenceherein for the purposes or subject matter referenced herein.Pharmaceutically acceptable salts of the compounds of this inventioninclude those derived from suitable inorganic and organic acids andbases. Examples of pharmaceutically acceptable, nontoxic acid additionsalts are salts of an amino group formed with inorganic acids such ashydrochloric acid, hydrobromic acid, phosphoric acid, sulfuric acid andperchloric acid or with organic acids such as acetic acid, oxalic acid,maleic acid, tartaric acid, citric acid, succinic acid or malonic acidor by using other methods used in the art such as ion exchange. Otherpharmaceutically acceptable salts include adipate, alginate, ascorbate,aspartate, benzenesulfonate, benzoate, bisulfate, borate, butyrate,camphorate, camphorsulfonate, citrate, cyclopentanepropionate,digluconate, dodecylsulfate, ethanesulfonate, formate, fumarate,glucoheptonate, glycerophosphate, gluconate, hemisulfate, heptanoate,hexanoate, hydroiodide, 2-hydroxy-ethanesulfonate, lactobionate,lactate, laurate, lauryl sulfate, malate, maleate, malonate,methanesulfonate, 2-naphthalenesulfonate, nicotinate, nitrate, oleate,oxalate, palmitate, pamoate, pectinate, persulfate, 3-phenylpropionate,phosphate, picrate, pivalate, propionate, stearate, succinate, sulfate,tartrate, thiocyanate, p-toluenesulfonate, undecanoate, valerate salts,and the like. Salts derived from appropriate bases include alkali metal,alkaline earth metal, ammonium and N⁺(C₁₋₄alkyl)₄ salts. Representativealkali or alkaline earth metal salts include sodium, lithium, potassium,calcium, magnesium, and the like. Further pharmaceutically acceptablesalts include, when appropriate, nontoxic ammonium, quaternary ammonium,and amine cations formed using counter ions such as halide, hydroxide,carboxylate, sulfate, phosphate, nitrate, loweralkyl sulfonate and arylsulfonate.

In certain embodiments, the compound is in the form of a hydrate orsolvate. The term “hydrate” as used herein refers to a compoundnon-covalently associated with one or more molecules of water. Likewise,the term “solvate” refers to a compound non-covalently associated withone or more molecules of an organic solvent.

Uses of the prodrugs of the compounds described herein for treating painis also within the scop of the present disclosure. Examples of prodrugsinclude esters and other pharmaceutically acceptable derivatives, which,upon administration to a subject, are capable of providing the indolecompounds described above (see Goodman and Gilman's, The Pharmacologicalbasis of Therapeutics, 8th ed., McGraw-Hill, Int. Ed. 1992,“Biotransformation of Drugs”).

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimit of that range and any other stated or intervening value in thatstated range, is encompassed within the invention. The upper and lowerlimits of these smaller ranges may independently be included in thesmaller ranges, and are also encompassed within the invention, subjectto any specifically excluded limit in the stated range. Where the statedrange includes one or both of the limits, ranges excluding either orboth of those included limits are also included in the invention.

Other objects, features and advantages of the present invention willbecome apparent from the following detailed description. It should beunderstood, however, that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings form part of the present specification and areincluded to further demonstrate certain aspects of the presentdisclosure, the inventions of which can be better understood byreference to one or more of these drawings in combination with thedetailed description of specific embodiments presented herein.

FIG. 1 shows the effects of the compound T1-11 in inhibition ofacid(ASIC3)-induced chronic muscle pain in mice; wherein theASIC3-dependent chronic muscle pain was induced by repeated injectionsof acid saline (pH 4.0, 20 μl) to one side of gastrocnemius muscle. Asfound in FIG. 1, the first acid-injection induced a transienthyperalgesia in mouse hind paws that attenuated at 24 h, whereas thesecond acid injection (in 5 days) caused a bilateral long-lastingmechanical hyperalgesia for more than 2 weeks (left panel). Theco-injection of acid and T1-11 (middle panel) or APETx2 (a selectiveASIC3 antagonist, right panel) abolished the transient hyperalgesia andprevented the development of chronic hyperalgesia induced by repeatedacid injection.

FIG. 2 shows that the compound T1-11 induced an outward current inmuscle nociceptors. Panel A: a diagram showing that the compound T1-11elicited a slow inactivating outward current (I_(T1-11)) in adose-dependent manner in muscle nociceptor expressing SP-induced outward(I_(SP-O)). Panel B: a chart showing the peak whole-cell currentamplitude as a function of I_(SP-O), and dose-dependent (0.1, 1, 3, and10 μM) of I_(SP-O) with an EC₅₀ of 2.6 μM is shown (n=27). Panel C: apanel showing the peak whole-cell current as a function of I_(T1-11),and dose-dependent (1, 3, 10, 30, and 100 nM) of I_(T1-11) with an EC₅₀of 1.3 nM is shown (n=11).

FIG. 3 shows the effect of some adenosine analogs incluidng T1-11 andJMF1998, 1907 and 2665 on SP-sensitive muscle nociceptors, wherein theupper panel shows the representative traces for adenosine analogs,JMF1998, 1907 and 2665, mediated outward currents in a musclenociceptor; and the lower panel shows the relative potency of T1-11,JMF1998, 1907 and 2665, to induce an outward current in musclenociceptors as compared with SP (n=8).

FIG. 4 shows the effects of the compound CGS21680 on acid-induced musclepain; wherein a co-injection of the compound CGS21680 (1 nmole, i.m.)and acidic saline partially inhibited acid-induced hyperalgesia, and aco-injection of an A3 agonist, IB-MECA (1 nmole, i.m.) as a control hasno effect on acid-induced hyperalgesia.

FIG. 5 provides a schematic model of antinociception in ASIC3-expressingmuscle nociceptors, showing that the adenosine analogs according to theinvention, such as the compound T1-11, target on a novel analgesicpathway.

FIG. 6 shows that whole-cell patch clamp recordings revealed theinhibition of ASIC3-mediated current by the compound T1-11. Pane A: adiagram showing that no acid-induced current was found in CHO cellswithout ASIC3 transfection. Panel B: a diagram showing that theacid-induced current was blocked by salicylic acid (SA, a selectiveantagonist for ASIC3), and T1-11 in CHO cells transfected with ASIC3.Panel C: a diagram showing that the compound T1-11 (10 nM) inhibitedacid-induced current in all ASIC3-expressing muscle nocicptors (n=9).

FIG. 7 shows that the compound T1-11 mediated currents in muscle DRGneurons; wherein the upper panel shows the T1-11-inducedelectrophysiological responses resulting from superfusion of 100 nMT1-11 for 4 s in GM-afferent DRG neurons and non-GM-afferent DRG neurons(including the number of neurons and percentage for each type ofresponses); and the lower panel shows the mean peak outward current ofT1-11 (100 nM), that is similar to that of 3 μM substance P.

FIG. 8 shows that the compound T1-11 had the analgesic effect on amodified acid-induced chronic muscle pain model. Panel A: a diagramshowing that mice were first received an intramuscular injection ofgenistein (a tyrosine kinase inhibitor) and an acid saline to one sideof gastrocnemius muscle, and then pain behaviors were assayed by usingvon-Frey filament test at 4 hr (DO) and until 29 days (D29) after acidinjection. Panel B: is a chart showing that the single acid injectioninduced long-lasting chronic hyperalgesia in mice with genisteinpretreatment (open circles, n=5), but only transient hyperalgesia inmice without genistein pretreatment (filled circles, n=4). Panel C: achart showing the effect of genistein pretreatment that can be reversedby co-injection of acid and the compound T1-11 (open circle, n=6), whichonly showed the transient hyperalgeisa, but not the vehicle (filledcircles, n=5).

FIG. 9 shows the analgesic effect of the compound T1-11 on a mouse modelof fibromyalgia; wherein T1-11 (30 ug/kg) had analgesic effect on micetreated with ICS. Mechanical hyperalgesia was assessed by applying a 0.2mN von Frey filament to the plantar surface of both hind paws. For eachpaw, the filament was applied for 5 times at 30-s intervals.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, it is unexpectedly found thatadenosine analogs, which are effective for the treatment of pain throughactivation of neurokinin 1 (NK1) receptor signaling pathway in musclenociceptors, thereby inducing the activation of activation of M-typepotassium channel to induce outward currents. It is also found that theoutward current is induced by M-type potassium channel in muscleafferent DRG neurons, and the activation of M-type potassium channel ismediated by NK1 receptor signaling in muscle afferent DRG neurons.

Accordingly, the invention provides a use in the manufacture of amedicament for treating pain of an adenonsine analog that activates NK1receptor signaling, thereby inducing outward current.

In the invention, mice lacking SP signaling were used to determine thecontribution of SP to muscle pain sensitivity, and it is found that incontrast to the neurotransmitter's usual excitatory role, mice withoutSP signaling showed increased pain sensitivity after intramuscular acidinjections as compared with mice that had normal SP signaling. Increasedsensitivity to muscle pain was noted in mice lacking the gene for SPsignaling as well as mice administered compounds designed to bind SPreceptors.

It was also found in the invention that the antinociceptive effect of SPsignaling involved the activation of NK1 receptor on muscle nociceptors.FIG. 5 illustrates a schematic model of the T1-11 antinociception inASIC3-expressing muscle nociceptors. When tissue acidosis occurs inmuscle, protons depolarize the muscle afferents, and T1-11 acts on theNK1 associated with receptor in the local nerve terminals. The NK1receptors on muscle afferents are coupled with an unconventional signalpathway by activating M channels via a G-protein-independent, tyrosinekinase-dependent manner.

Accordingly, the invention provides a use in the manufacture of amedicament for treating pain of an adenonsine analog that activates NK1receptor signaling, thereby inducing outward current.

It is evidenced the adenosine analog according to the invention iseffective for treating acid-induced pain in term of the effects of T1-11in inhibition of acid-sensing ion channel 3 (ASIC3) in musclenociceptors. That is, the pain may include the pain associated withtissue acidosis, and the pain is associated with muscular origin, suchas in muscle afferent DRG neurons. Accordingly, it is expected that thepain to be treated includes acid-induced pain, sich as acid-inducedmuscle pain, particularly an acid-induced chronic muscle pain.

According to the invention, the pain may include inflammatory pain,cancer pain, chest pain, back pain, facial pain, joint pain, muscularpain syndromes, neuropathic pain, peripheral pain, cancer and tumorpain, sympathetic pain, postoperative pain, and post-traumatic pain. Insome embodiments, the pain is fibromyalgia, myofascial pain, bladderpain syndrome or pain caused by irritable bowel syndrome.

In the invention, it was evideced in Examples that some adenosineanalogs, such as an adenosine analog having the formula T1-11 (“thecompound T1-11” or “T1-11”), was proven to be effective in treatingpain, particularly acid-induced pain.

The compound T1-11 is known as2-(6-(4-hydroxybenzylamino)-9H-purin-9-yl)-5-(hydroxymethyl)-tetrahydrofuran-3,4-diol,which may be isolated from Gastrodia extract, such as from the roots.(See also U.S. Pat. No. 7,351,434 at col. 20, lines 4-22.) The compoundT1-11 was proven to activate neurokinin 1 (NK1) receptor signaling, andto be antinociceptive in ASIC3-mediated pain model. A low dose of T1-11(4 pmole) still had analgesic effects on acid-induced chronic musclepain models in mice (see FIG. 1). It was indicated that T1-11 mediatedan outward current in SP-sensitive ASIC3-expressing muscle nociceptorsand thus inhibited acid-induced ASIC3 activation (see FIG. 2(A)). TheEC₅₀ of T1-11 for outward current is 1.3 nM as compared with SP of 2.6μM (see FIGS. 2(B) & 2(C)). In addition to the compound T1-11, otheradenosine analogs were also shown to mediate an outward current aspotent as SP in muscle nociceptors (see Figure. 3).

According to the invention, the adenosine analog is a compound ofFormula (I):

or a pharmaceutically acceptable salt, solvate, or hydrate thereof;wherein:

X is O, S or CH₂;

R¹ is selected from the group consisting of NHR⁴, NH(CH₂)_(n)R⁴,NH—NHR⁴, NHCONHR⁴, NH—OR⁴, O—NHR⁴, and SR⁴;

R² is selected from the group consisting of hydrogen (H), halogen,cyano, OR⁴, NHR⁴, substituted or unsubstituted alkyl, substituted orunsubstituted alkenyl, substituted or unsubstituted alkynyl, substitutedor unsubstituted cycloalkyl, substituted or unsubstituted aryl (Ar),substituted or unsubstituted aralkyl, and a substituted or unsubstitutedheterocyclyl;

R³ is selected from the group consisting of halomethyl, hydroxymethyl(HOCH₂), alkoxymethyl (R⁴OCH₂), azidomethyl (N₃CH₂), aminomethyl(H₂NCH₂), substituted or unsubstituted aminomethyl, amidomethyl(H₂NCOCH₂), sulfanylmethyl (R⁴S), sulfonylmethyl (R⁴SO₂),triazolylmethyl, cyanomethyl (N≡CCH₂), cyano, substituted orunsubstituted carbonyl (R⁴CO), COOH, substituted or unsubstitutedaminocarbonyl (R⁴HNCO), substituted or unsubstituted alkynyl, andsubstituted or unsubstituted tetrazole;

n is 1, 2 or 3;

each instance of R⁴ is independently selected from the group consistingof H, alkyl, cycloalkyl, substituted or unsubstituted Ar, substituted orunsubstituted aralkyl, and a substituted or unsubstituted heterocyclyl;

Ar is selected from the group consisting of substituted or unsubstitutedphenyl, substituted or unsubstituted polyarene, and a substituted orunsubstituted heterocycle.

In some embodiments, R² is hydrogen. In some embodiments, R² is halogen.In some embodiments, R² is cyano. In some embodiments, R² is OR⁴. Insome embodiments, R² is NHR⁴. In some embodiments, R² is substituted orunsubstituted alkyl. In some embodiments, R² is substituted orunsubstituted alkenyl. In some embodiments, R² is substituted orunsubstituted alkynyl. In some embodiments, R² is substituted orunsubstituted cycloalkyl. In some embodiments, R² is substituted orunsubstituted aryl. In some embodiments, R² is substituted orunsubstituted aralkyl. In some embodiments, R² is a hydrocarbon chainwherein the carbon unit is substituted by one or more aryl groups. Insome embodiments, R² is C₁₋₁₀ hydrocarbon chain with the carbon unitsubstituted by one or more aryl groups. In some embodiments, R² issubstituted or unsubstituted heterocyclyl. In some embodiments, R² is 5-or 6-membered ring or fused ring containing at least one nitrogen,oxygen or sulfur heteroatoms.

In some embodiments, R⁴ is substituted or unsubstituted aralkyl. In someembodiments, R⁴ is a hydrocarbon chain with the carbon unit substitutedby one or more aryl groups. In some embodiments, R⁴ is a C₁₋₁₀hydrocarbon chain with the carbon unit substituted by one or more arylgroups. In some embodiments, R⁴ is substituted or unsubstitutedheterocyclyl. In some embodiments, R⁴ is 5- or 6-membered ring or fusedring containing at least one nitrogen, oxygen or sulfur heteroatoms.

In some embodiments, Ar is substituted or unsubstituted phenyl. In someembodiments, Ar is substituted or unsubstituted polyarene. In someembodiments, Ar is substituted or unsubstituted heterocycle. In someembodiments, Ar is substituted or unsubstituted heterocycle of 5- or6-membered ring or fused ring containing at least one nitrogen, oxygenor sulfur heteroatoms.

In some embodiments of the invention, the adenosine analogs arerespectively the compounds of Formula (II), Formula (III), and Formula(IV) as listed in Table 1 below, including but not limited to someexamples, JMF1998, JMF2665, JMF1907 and CGS21680. The compoundsdescribed herein include salts, solvates, hydrates forms thereof.

TABLE 1 Compound Example

The compounds described herein can be prepared by conventional chemicaltransformations (including protecting group methodologies), e.g., thosedescribed in R. Larock, Comprehensive Organic Transformations, VCHPublishers (1989); T. W. Greene and P. G. M. Wuts, Protective Groups inOrganic Synthesis, 3rd Ed., John Wiley and Sons (1999); L. Fieser and M.Fieser, Fieser and Fieser's Reagents for Organic Synthesis, John Wileyand Sons (1994); and L. Paquette, ed., Encyclopedia of Reagents forOrganic Synthesis, John Wiley and Sons (1995) and subsequent editionsthereof.

A compound thus synthesized can be further purified by flash columnchromatography, high performance liquid chromatography, crystallization,or any other suitable methods.

Alternatively, the adenosine analog described herein (e.g., T1-11) canbe isolated from its natural source (e.g., extracted from a Gastrodia).In one example, compound T1-11 can be isolated from a Gastradia extract.

A listing of references related to the present invention, the contentsof which are incorporated by reference for the purposes or subjectmatter referenced herein, includes: (1) U.S. Pat. No. 7,351,434, inpart, disclosing the compound T1-11 and its chemical structure; (2)Huang et al., A new drug design targeting the adenosinergic system forHuntington's disease (PLoS ONE 2011; 6 (6) 220934, describing theisolation of T1-11 and the dual function of T1-11, and the potentialapplication of T1-11 for treating Huntington's disease); (3) Lin et al.,An antinociceptive role for substance P in acid-induced chronic musclepain. Proc Natl Acad Sci USA., 2012, describing that intramuscularsubstance P mediates an unconventional NK1 receptor signal pathway toinhibit acid activation in muscle nociceptors, which results in anunexpected anti-nociceptive effect against chronic mechanicalhyperalgesia induced by repeated intramuscular acid injection; (4) Devalet al., Acid-sensing ion channels in postoperative pain. J Neurosci31:6059-6066, 2011, describing that muscle nociceptors expressing ASIC3was responsible for postoperative pain. Applying ASIC3 selectiveantagonist can effectively block the postoperative pain. Otherpublications cited herein are also incorporated by reference for thepurposes or subject matter referenced herein.

The compounds mentioned herein may contain a non-aromatic double bondand one or more asymmetric centers. Thus, they can occur as racematesand racemic mixtures, single enantiomers, individual diastereomers,diastereomeric mixtures, and cis- or trans-isomeric forms. All suchisomeric forms are contemplated.

Pharmaceutical Compositions

Pharmaceutical compositions of the present invention and for use inaccordance with the present invention may include a pharmaceuticallyacceptable excipient or carrier. As used herein, the term“pharmaceutically acceptable carrier” or “pharmaceutically acceptableexcipient” means a non-toxic, inert solid, semi-solid or liquid filler,diluent, encapsulating material or formulation auxiliary of any type.Remington's Pharmaceutical Sciences, Sixteenth Edition, E. W. Martin(Mack Publishing Co., Easton, Pa., 1980) discloses various excipientsused in formulating pharmaceutical compositions and known techniques forthe preparation thereof. Some examples of materials which can serve aspharmaceutically acceptable carriers are sugars such as lactose,glucose, and sucrose; starches such as corn starch and potato starch;cellulose and its derivatives such as sodium carboxymethyl cellulose,ethyl cellulose, and cellulose acetate; powdered tragacanth; malt;gelatin; talc; excipients such as cocoa butter and suppository waxes;oils such as peanut oil, cottonseed oil; safflower oil; sesame oil;olive oil; corn oil and soybean oil; glycols such as propylene glycol;esters such as ethyl oleate and ethyl laurate; agar; detergents such asTween 80; buffering agents such as magnesium hydroxide and aluminumhydroxide; alginic acid; pyrogen-free water; isotonic saline; Ringer'ssolution; ethyl alcohol; and phosphate buffer solutions, as well asother non-toxic compatible lubricants such as sodium lauryl sulfate andmagnesium stearate, as well as coloring agents, releasing agents,coating agents, sweetening, flavoring and perfuming agents,preservatives and antioxidants can also be present in the composition,according to the judgment of the formulator. The pharmaceuticalcompositions of this invention can be administered to humans and/or toanimals, orally, rectally, parenterally, intracisternally,intravaginally, intranasally, intraperitoneally, topically (as bypowders, creams, ointments, or drops), bucally, or as an oral or nasalspray.

Liquid dosage forms for oral administration include pharmaceuticallyacceptable emulsions, microemulsions, solutions, suspensions, syrups,and elixirs. In addition to the active ingredients (i.e.,microparticles, nanoparticles, liposomes, micelles, polynucleotide/lipidcomplexes), the liquid dosage forms may contain inert diluents commonlyused in the art such as, for example, water or other solvents,solubilizing agents and emulsifiers such as ethyl alcohol, isopropylalcohol, ethyl carbonate, ethyl acetate, benzyl alcohol, benzylbenzoate, propylene glycol, 1,3-butylene glycol, dimethylformamide, oils(in particular, cottonseed, groundnut, corn, germ, olive, castor, andsesame oils), glycerol, tetrahydrofurfuryl alcohol, polyethylene glycolsand fatty acid esters of sorbitan, and mixtures thereof. Besides inertdiluents, the oral compositions can also include adjuvants such aswetting agents, emulsifying and suspending agents, sweetening,flavoring, and perfuming agents.

Injectable preparations, for example, sterile injectable aqueous oroleaginous suspensions may be formulated according to the known artusing suitable dispersing or wetting agents and suspending agents. Thesterile injectable preparation may also be a sterile injectablesolution, suspension, or emulsion in a nontoxic parenterally acceptablediluent or solvent, for example, as a solution in 1,3-butanediol. Amongthe acceptable vehicles and solvents that may be employed are water,Ringer's solution, U.S.P. and isotonic sodium chloride solution. Inaddition, sterile, fixed oils are conventionally employed as a solventor suspending medium. For this purpose any bland fixed oil can beemployed including synthetic mono- or diglycerides. In addition, fattyacids such as oleic acid are used in the preparation of injectables. Incertain embodiments, the particles are suspended in a carrier fluidcomprising 1% (w/v) sodium carboxymethyl cellulose and 0.1% (v/v) Tween80.

The injectable formulations can be sterilized, for example, byfiltration through a bacteria-retaining filter, or by incorporatingsterilizing agents in the form of sterile solid compositions which canbe dissolved or dispersed in sterile water or other sterile injectablemedium prior to use.

In order to prolong the effect of a drug, it is often desirable to slowthe absorption of the drug from subcutaneous or intramuscular injection.This may be accomplished by the use of a liquid suspension orcrystalline or amorphous material with poor water solubility. The rateof absorption of the drug then depends upon its rate of dissolutionthat, in turn, may depend upon crystal size and crystalline form.Alternatively, delayed absorption of a parenterally administered drugform is accomplished by dissolving or suspending the drug in an oilvehicle. Injectable depot forms are made by forming microencapsulematrices of the drug in biodegradable polymers such aspolylactide-polyglycolide. Depending upon the ratio of drug to polymerand the nature of the particular polymer employed, the rate of drugrelease can be controlled. Examples of other biodegradable polymersinclude poly(orthoesters) and poly(anhydrides). Depot injectableformulations are also prepared by entrapping the drug in liposomes ormicroemulsions which are compatible with body tissues.

Compositions for rectal or vaginal administration are preferablysuppositories which can be prepared by mixing the particles withsuitable non-irritating excipients or carriers such as cocoa butter,polyethylene glycol, or a suppository wax which are solid at ambienttemperature but liquid at body temperature and therefore melt in therectum or vaginal cavity and release the particles.

Solid dosage forms for oral administration include capsules, tablets,pills, powders, and granules. In such solid dosage forms, the particlesare mixed with at least one inert, pharmaceutically acceptable excipientor carrier such as sodium citrate or dicalcium phosphate and/or a)fillers or extenders such as starches, lactose, sucrose, glucose,mannitol, and silicic acid, b) binders such as, for example,carboxymethylcellulose, alginates, gelatin, polyvinylpyrrolidinone,sucrose, and acacia, c) humectants such as glycerol, d) disintegratingagents such as agar-agar, calcium carbonate, potato or tapioca starch,alginic acid, certain silicates, and sodium carbonate, e) solutionretarding agents such as paraffin, f) absorption accelerators such asquaternary ammonium compounds, g) wetting agents such as, for example,cetyl alcohol and glycerol monostearate, h) absorbents such as kaolinand bentonite clay, and i) lubricants such as talc, calcium stearate,magnesium stearate, solid polyethylene glycols, sodium lauryl sulfate,and mixtures thereof. In the case of capsules, tablets, and pills, thedosage form may also comprise buffering agents.

Solid compositions of a similar type may also be employed as fillers insoft and hard-filled gelatin capsules using such excipients as lactoseor milk sugar as well as high molecular weight polyethylene glycols, andthe like.

The solid dosage forms of tablets, dragees, capsules, pills, andgranules can be prepared with coatings and shells such as entericcoatings and other coatings well known in the pharmaceutical formulatingart. They may optionally contain opacifying agents and can also be of acomposition that they release the active ingredient(s) only, orpreferentially, in a certain part of the intestinal tract, optionally,in a delayed manner. Examples of embedding compositions which can beused include polymeric substances and waxes.

Solid compositions of a similar type may also be employed as fillers insoft and hard-filled gelatin capsules using such excipients as lactoseor milk sugar as well as high molecular weight polyethylene glycols andthe like.

Dosage forms for topical or transdermal administration of an inventivepharmaceutical composition include ointments, pastes, creams, lotions,gels, powders, solutions, sprays, inhalants, or patches. The particlesare admixed under sterile conditions with a pharmaceutically acceptablecarrier and any needed preservatives or buffers as may be required.Ophthalmic formulation, ear drops, and eye drops are also contemplatedas being within the scope of this invention.

In certain embodiments, the pharmaceutically acceptable topicalformulations of the invention comprise at least a compound of theinvention and a penetration enhancing agent. The choice of topicalformulation will depend or several factors, including the condition tobe treated, the physicochemical characteristics of the inventivecompound and other excipients present, their stability in theformulation, available manufacturing equipment, and costs constraints.As used herein the term “penetration enhancing agent” means an agentcapable of transporting a pharmacologically active compound through thestratum coreum and into the epidermis or dermis, preferably, with littleor no systemic absorption. A wide variety of compounds have beenevaluated as to their effectiveness in enhancing the rate of penetrationof drugs through the skin. See, for example, Percutaneous PenetrationEnhancers, Maibach H. I. and Smith H. E. (eds.), CRC Press, Inc., BocaRaton, Fla. (1995), which surveys the use and testing of various skinpenetration enhancers, and Buyuktimkin et al., Chemical Means ofTransdermal Drug Permeation Enhancement in Transdermal and Topical DrugDelivery Systems, Gosh T. K., Pfister W. R., Yum S. I. (Eds.),Interpharm Press Inc., Buffalo Grove, Ill. (1997). In certain exemplaryembodiments, penetration agents for use with the invention include, butare not limited to, triglycerides (e.g., soybean oil), aloe compositions(e.g., aloe-vera gel), ethyl alcohol, isopropyl alcohol,octolyphenylpolyethylene glycol, oleic acid, polyethylene glycol 400,propylene glycol, N-decylmethylsulfoxide, fatty acid esters (e.g.,isopropyl myristate, methyl laurate, glycerol monooleate, and propyleneglycol monooleate), and N-methyl pyrrolidone.

Transdermal patches have the added advantage of providing controlleddelivery of a compound to the body. Such dosage forms can be made bydissolving or dispensing the microparticles or nanoparticles in a propermedium. Absorption enhancers can also be used to increase the flux ofthe compound across the skin. The rate can be controlled by eitherproviding a rate controlling membrane or by dispersing the particles ina polymer matrix or gel.

In the invention, the pharmaceutical compositions may be in the form ofointments, pastes, creams, lotions, gels, powders, solutions, sprays,inhalants. or patches. In certain exemplary embodiments, formulations ofthe compositions according to the invention are creams, which mayfurther contain saturated or unsaturated fatty acids such as stearicacid, palmitic acid, oleic acid, palmito-oleic acid, cetyl or oleylalcohols, stearic acid being particularly preferred. Creams of theinvention may also contain a non-ionic surfactant, for example,polyoxy-40-stearate. In certain embodiments, the active component isadmixed under sterile conditions with a pharmaceutically acceptableexcipient and any needed preservatives or buffers as may be required.Ophthalmic formulations, eardrops, and eye drops are also contemplatedas being within the scope of this invention. Additionally, the presentinvention contemplates the use of transdermal patches, which have theadded advantage of providing controlled delivery of a compound to thebody. Such dosage forms are made by dissolving or dispensing thecompound in the proper medium. As discussed above, penetration enhancingagents can also be used to increase the flux of the compound across theskin. The rate can be controlled by either providing a rate controllingmembrane or by dispersing the compound in a polymer matrix (e.g., PLGA)or gel.

The ointments, pastes, creams, and gels may contain excipients such asanimal and vegetable fats, oils, waxes, paraffins, starch, tragacanth,cellulose derivatives, polyethylene glycols, silicones, bentonites,silicic acid, talc, and zinc oxide, or mixtures thereof.

Powders and sprays can contain excipients such as lactose, talc, silicicacid, aluminum hydroxide, calcium silicates, and polyamide powder, ormixtures of these substances. Sprays can additionally contain customarypropellants such as chlorofluorohydrocarbons.

It will also be appreciated that the compounds and pharmaceuticalcompositions of the invention can be formulated and employed incombination therapies, that is, the compounds and pharmaceuticalcompositions can be formulated with or administered concurrently with,prior to, or subsequent to, one or more other desired therapeutics ormedical procedures. The particular combination of therapies(therapeutics or procedures) to employ in a combination regimen willtake into account compatibility of the desired therapeutics and/orprocedures and the desired therapeutic effect to be achieved. It willalso be appreciated that the therapies employed may achieve a desiredeffect for treating pain.

It will also be appreciated that certain of the compounds of theinvention can exist in free form for treatment, or where appropriate, asa pharmaceutically acceptable derivative thereof. According to thepresent invention, a pharmaceutically acceptable derivative includes,but is not limited to, pharmaceutically acceptable salts, esters, saltsof such esters, or a prodrug or other adduct or derivative of a compoundof this invention which upon administration to a patient in need iscapable of providing, directly or indirectly, a compound as otherwisedescribed herein, or a metabolite or residue thereof.

Accordingly, the invention also provides a pharmaceutical compositionfor treating pain, comprising:

(a) an adenosine analog as defined herein (e.g., formula I, II, III, orIV such as compound T1-11, JMF1907, JMF1998, JMF2665, and CGS21680), and

(b) a further active agent for treating pain, wherein the further activeagent is different from the adenosine analog.

Methods of Treatment

The present invention provides a method for treating pain comprisingadministering to a subject in need thereof a therapeutically effectiveamount of an adenosine analog, or a pharmaceutical composition asdefined herein. The compounds according to the invention can enhanceoutward current induced by M-type potassium channel in muscle neurons.The activation of NK1 receptor signaling produces beneficial therapeuticeffects on pain management.

In the invention, the pain to be treated may be associated withcardiovascular disease, stroke-induced neural damage, arthritis, cancer,inflammation, infection, oropharengeal diseases or damage, traumaticinjuries, acute and chronic cough, gastrointestinal disorders, centralnervous system disorders, psychiatric diseases or manifestations.

The compounds of the invention are preferably formulated in dosage unitform for ease of administration and uniformity of dosage. The expression“dosage unit form” as used herein refers to a physically discrete unitof therapeutic agent appropriate for the patient to be treated. It willbe understood, however, that the total daily usage of the compounds andcompositions of the present invention will be decided by the attendingphysician within the scope of sound medical judgment. The specifictherapeutically effective dose level for any particular patient ororganism will depend upon a variety of factors including the disorderbeing treated and the severity of the disorder; the activity of thespecific compound employed; the specific composition employed; the age,body weight, general health, sex, and diet of the subject; the time ofadministration, mute of administration, and rate of excretion of thespecific compound employed; the duration of the treatment; drugs used incombination or coincidental with the specific compound employed; andlike factors well known in the medical arts (see, for example, Goodmanand Gilman's The Pharmacological Basis of Therapeutics, Tenth Edition,A. Gilman, J. Hardman and L. Limbird, eds., McGraw-Bill Press, 155-173,2001, which is incorporated herein by reference in its entirety).

Examples Materials and Methods

Animals. Adult (8- to 12-wk-old) C57/BL6 mice was used. All proceduresfollowed the Guide for the Use of Laboratory Animals (National AcademyPress, Washington DC, USA) and were approved by the Institutional AnimalCare and Use Committee of Academia Sinica. We aimed to minimize thenumber of animals used and their suffering without compromising thequality of the experiments. The generation and genotyping of Tac1^(−/−)mice and Asic3^(−/−) mice were as described. Both null mutant mice werebackcrossed to C57/BL6 for 10 generations to establish a congenicstrain. Congenic Tac1^(−/−) Asic3^(−/−) mice were offspring ofTac1^(+/−) and Asic3^(+/−) intercrosses.

Mouse model of fibromyalgia. To induce fibromyalgia-like symptoms, micewere treated with intermittent cold stress, which produces long-lasting(more than 2 weeks) thermal hyperalgesia and mechanical allodynia,predominantly in females. Method: Mice were placed on stainless meshplate in a cold room at 4° C. overnight (from 4:30 pm to 10:00 am),followed by intermittent cold stress with environment temperaturesalternating between 24 and 4° C. every 30 min, from 10:00 am to 4:30 pm.These procedures were repeated twice. On day 3, the mice were adapted to24 C for 1 h before behavioral testing.

Behavioral Assays. Mice received an intramuscular acid injection in thegastrocnemius muscle (GM) containing 20 pi acid saline (pH 4.0) with orwithout (Sar⁹, Met(O₂)¹¹)-substance P (SP; 4, 10, or 40 μM) or 100 μMRP67580 or 200 μM XE991. Mechanical hyperalgesia was assessed byapplying a 0.2-mN von Frey filament to the plantar surface of both hindpaws of mice. Mice were acclimatized in an acrylic cubicle for 60 minbefore testing. A positive response was defined as the foot lifting whenthe von Frey filament was applied. For each paw, the filament wasapplied 5 times at 30-sec intervals. Responses of the paw to mechanicalstimuli were measured before injection and at 4 and 24 hr and 5 daysafter the first acid injection (day 0) and at 4, 24, and 72 hr and 1week after the second acid injection (day 5). For single-injectionexperiments, responses to mechanical stimuli were measured before theinjection, at 4 hr and at 1, 3, 5, 7, 9, 11, 13, 15 and 22 days afterthe injection or at 4, 24, 48 hr and 7 and 14 days after the injection.NK1-selective agonist ((Sar⁹, Met(O₂)¹¹)-SP) was from Sigma Chemical(St. Louis, Mo.). NK1-selective antagonist (RP67580) and XE991 were fromTocris (Avonmouth, UK). The experimenters were blinded to theexperimental manipulations. The person who conducted von Frey test hadno information of the mouse genotypes or drug injections.

Plasma Extravasation. Mice were intraperitoneally injected with 1% EvansBlue dye (EB, E2129-10 G Sigma) (W/V in phosphate buffered saline),which was sterilized by passage through Millex-GS 0.22-μm filter(Millipore). Then 24 hr later, mice were injected with 20 μl solution(pH 7.4 saline, pH 4.0 saline, 40 μM SM-SP, or 20% mustard oil) into theleft GM. At 30 min after intramuscular injection, the right and left GMwere individually dissected, weighed, diced, and placed in 4 ml of 99%formamide at room temperature (21-25° C.) for 72 hr. The samples werecentrifuged at 2,000 rpm for 20 min. The absorbance of the supernatantwas determined spectrophotometrically at 620-nm wavelength. The dyecontent of samples was calculated from a standard curve of Evans Blueconcentrations. Comparison between groups involved Mann-Whitney test.Drugs were purchased from Sigma Chemical.

Dorsal Root Ganglion (DRG) Primary Culture. To retrograde-tracemuscle-afferent DRG neurons, mice were injected with 4% Fluorogold(Fluorochrome, Denver, Colo.) into the GM of both legs for 5 to 7 days,then lumbar DRG neurons were dissected and removed from both sides andplaced in a tube for digestion with 1 ml DMEM containing 0.125% type 1collagenase for 90 min and 0.25% trypsin for 20 min at 37° C. Thedigested DRG neurons were washed with fetal calf serum (FCS)-free DMEMor DMEM containing 10% FCS during each treatment. Fully digested DRGswere triturated and plated on poly-L-lysine-coated cover slides. Cellcultures were maintained in a 5% CO2 incubator at 37° C.

Whole-Cell Patch-Clamp Recording. Whole-cell patch-clamp recordings ofmuscle-afferent neurons involved use of Axopatch MultiClamp 700B (AxonInstruments). Neurons with membrane potential >−40 mV were discarded.The bridge was balanced in current-clamp recording, and the seriesresistance was compensated 70% in voltage-clamp recording with Axopatch700B compensation circuitry. All experiments were performed at roomtemperature (21-25° C.) and completed within 30 hr post-seeding. Unlessspecifically mentioned, the patch pipettes were prepared in 1-5 MΩ andfilled with internal solution containing (in mM) 100 KCl, 2 Na_(z)-ATP,0.3 Na₃-GTP, 10 EGTA, 5 MgCl₂, and 40 HEPES, adjusted to pH 7.4 withKOH. Recording cells were superfused in artificial cerebrospinal fluid(ACSF) by control with gravitational force. The ACSF contained (in mM)130 NaCl, 5 KCl, 1 MgCl₂, 2 CaCl₂, 10 glucose, and 20 HEPES, adjusted topH 7.4 with NaOH. Osmolarity was adjusted to 300 mOsm. The acidic ACSFwas titrated to pH 6.8 by 1 M NaOH. SP was prepared from a 300-μM stocksolution to a final concentration of 3 μM in ACSF. In the experimentconfirming potassium channel as the ion channel responsible forgeneration of outward current, NaCl was replaced with Tetraethylammonium chloride and pH was adjusted with CsOH. If not specificallymentioned, drugs listed above were from Sigma Chemical (St. Louis, Mo.).Reagents used in the study of SP-induced outward current were from Sigma(GDP-β-S) or Tocris Bioscience (RP67580, GR159897, SB218795, genistein,PP1, sodium orthovanadate, daidzein, XE991 and Linopirdinedihydrochloride).

Effect of SP on Acid-Induced Electrophysiological Responses.Voltage-clamp mode was used to examine the effect of SP on acid-inducedcurrents in ASIC3-expressing DRG neurons. A total of 40 GM and 6 non-GMDRG neurons were recorded in voltage-clamp mode with Vm held at −70 mV.In this study, we focused on the salicylic acid (SA)-sensitive (SAS)neurons with acid-induced current inhibited by SA because they representASIC3-expressing neurons. DRG neurons were treated with pH 6.8 acidicACSF for 4 sec in each 30-sec time frame; 500 μM of SA in the bath wasused for cell-type selection. Next, SA-containing bath was replaced withnormal ACSF for 2 min, then a bath containing 3 μM SP for 3 min torecord acid-induced current in the presence of SP. Finally, theSP-containing bath was replaced with normal bath for another 3 min. Thenonhydrolysable form of GDP (GDP-β-S, 1 mM, from Sigma) was loaded inrecording pipettes and dialysed for 10 min before recording. The effectof GDP-β-S was examined in an SP-containing bath and stimulated withacid for 3 min. In the end, the bath was switched back to normal ACSFand stimulated for another 3 min. To validate whether the modulation ofSP on acid-induced current was NK1-receptor specific, acid-inducedcurrent was first recorded in a bath containing 10 μM RP67580 for 2 minas a control response. Next, the recording was performed in the bathcontaining both RP67580 and SP for 2 min, then one containing RP67580alone. Phosphotyrosine kinase was tested for its role in SP-directedmodulation on acid-induced current. Acid-induced current was recorded ina bath containing both SP and genistein (30 μM; Tocris), or both SP anddaidzein (30 μM; Tocris) for 3 min. In addition, recording was performedin SP- and genistein-only bath as positive and negative controls,respectively.

SP-Induced Currents. Voltage-clamp mode was used to detect SP-inducedcurrents, and neurons were held at −70 mV. SP in ACSF solutions (3 μM)was puffed through a valve controller-controlled glass pipette towardsthe recording neurons for 4 sec with a 30-sec interval. The procedurewas repeated at least 2 times to ensure consistent data. The SP-inducedcurrent tested under different pharmacological compounds was performedin triplicate. ACSF-containing compounds were superfused for 1 min toensure complete replacement of previous perfusate between treatments.Then, the test compounds were washed away with ACSF, and SP-inducedcurrents after the washout were examined 3 times. A neuron was definedas SP sensitive when the induced current was >10 pA (or <−10 pA with anoutward current). To further verify the independency of I_(SP-O) on GTP,Baclofen-induced GABA-B current served as a positive control. Arecording pipette containing 1 mM GDP-β-S was used in GTP dialysis. TheGABA-B current was induced by 100 μM Baclofen at the beginning ofdialysis (0, 1 and 2 min after whole-cell patch clamp). Then, Baclofenwas used to re-stimulate the dialyzed neurons after 10-min dialysis (10,11 and 12 min after whole-cell patch clamp). Then, SP was used to verifythe presence of I_(SP-O) in the absence of GTP.

Voltage-Gated Sodium Currents. To study the involvement of NK1 receptorand the M channel in modulating neuronal excitability under theinfluence of protons, mice were first injected with retrograde tracer 2days before the injection of acidic saline (pH 4.0, 20 μl) or incombination with 100 μM RP67580 or 200 μM XE991. The treated mice werethen killed and used for DRG culture 2 days later. For mice thatreceived 2 injections of pH 4.0 saline, the second injection was given 2days after the first injection and the mice were also killed 2 daysafter the second injection. DRG culture was as stated above and used forstudying the voltage-gated sodium currents. The internal solutioncontained (in mM) 10 NaCl, 110 CsCl, 20 tetraethylammonium-Cl, 2.5MgCl₂, 5 EGTA, 3 Mg₂ ⁺-ATP, and 5 HEPES, adjusted to pH 7.0 with CsOH.The external solution for voltage-gated sodium current contained (in mM)100 NaCl, 5 CsCl, 30 tetraethylammonium-Cl, 1.8 CaCl₂, 1 MgCl₂, 0.1CdCl₂, 25 glucose, 5 4-aminopyridine, and 5 HEPES, adjusted to pH 7.4with HCl. Osmolarity was adjusted to approximately 300 mOsm withglucose. DRG neurons with cell diameter between 30˜40 μm were selectedfor recording. The voltage-gated sodium currents were evoked by a30-msec test pulse at −40 mV from a holding potential of −80 mV.Recordings were performed in external solution with or without 200 nMtetrodotoxin (TTX; Tocris Bioscience, Avonmouth, UK).

Action Potential Threshold. The action potentials of GM DRG neurons ofdifferent experimental groups were evoked by various voltages, and thethreshold was defined as the beginning of the steep upward rise of theaction potential.

Data Analysis. Results are presented as mean±SEM and analyzed by use ofOrigin 8.0 (OriginLab, Northampton, MA). One-way ANOVA then Fisher LSDpost-hoc test was used to calculate differences between groups (FIG. 2).Other electrophysiological data were analyzed by paired or unpairedStudent's t test as appropriate. The Mann-Whitney U test was used tocompare withdrawal responses to von Frey filament in mice between beforeacid injection (baseline) and each time point after intramuscularacid-injection. A P<0.05 was considered statistically significant.

Results

T1-11 Analgesia

It was found that the compound T1-11 had analgesic effect onacid-induced chronic muscle pain, in which the muscle pain was inducedby repeated injection of acid saline (pH 4.0, 20 μl) to one side ofgastrocnemius muscle (GM). The first acid injection induced rapid,transient referred hyperalgesia, which declined after 24 h; a secondacid injection administered 5 day after the first induced long-lasting(>2 weeks) referred hyperalgesia. The acid-induced muscle pain isASIC3-dependent. Co-injection of acid with ASIC3 antagonist APETx2 (2pmole) at the first injection abolished the development of chronichyperalgesia induced by the second acid injection. T1-11 (4 pmole) hasthe similar potency with APETx2 in inhibition of the acid-inducedchronic hyperalgesia (FIG. 1).

The cellular basis of the T1-11 analgesia is that T1-11 induces anoutward current (I_(T1-11)) in ASIC3-positive muscle afferent DRGneurons that also express substance P (SP)-induced outward current(I_(SP-O)). The EC₅₀ of I_(T1-11) is 1.3 nM as compared with I_(SP-O)2.6 μM (FIG. 2).

T1-11 analogues, such as JMF1998, 1907, 2665, CGS21680, can also induceoutward currents in the ASIC3/SP-expressing muscle DRG neurons (seeFIGS. 3 and 4). Co-injection of A2AR agonist CGS21680 (I nmole, i.m.)and acidic saline partially inhibited acid-induced hyperalgesia, whereasco-injection of A3 agonist IB-MECA (1 nmole, i.m.) has no effect onacid-induced hyperalgesia.

A new schematic model of T1-11 antinociception in muscle nociceptors wasconcluded and illustrated in FIG. 5. When tissue acidosis occurs inmuscle, protons depolarize the muscle afferents. T1-11 acts on theNK1-associated receptor in the local nerve terminals. The NK1-associatedreceptors on muscle afferents are coupled with an unconventional signalpathway by activating M channels via a G-protein-independent, tyrosinekinase-dependent manner.

Whole-cell patch clamp recordings revealed the inhibition ofASIC3-mediated current by T1-11. In CHO cells transfected with ASIC3,the acid-induced current was blocked by salicylic acid (SA, a selectiveantagonist for ASIC3), and T1-11. (C) In all ASIC3-expressing musclenocicptors, T1-11 in low dose (10 nM) is enough to inhibit acid-inducedcurrent (see FIG. 6).

As shown in FIG. 7, the upper panel shows T1-11-mediated currents foundin muscle DRG neurons (see the upper panel), and T1-11-inducedelectrophysiological responses resulting from superfusion of 100 nMT1-11 for 4 s in GM-afferent DRG neurons and non-GM-afferent DRGneurons, including the number of neurons and percentage for each type ofresponses. The lower panel shows the mean peak outward current of T1-11(100 nM) is similar to that of 3 μM substance P.

T1-11 Pharmacology

The I_(T1-11) is predominantly expressed in muscle afferent DRG neuronsbut not other sensory neurons. We then determined the molecular basis ofI_(T1-11) in muscle nociceptors. I_(T1-11) is reversely inhibited by A3adenosine receptor antagonists (MRS1220, MRE3008F20) but not by A2Aadenosine receptor antagonist (ZM241385), indicating the involvement ofA3 adenosine receptors. Although T1-11 was known bound to A2A adenosinereceptors in neurons of central nervous system, we showed that I_(T1-11)is not changed in A2A^(−/−) muscle afferent DRG neurons. We also foundthat A3 adenosine receptor antagonist (MRS1220, 200 pmole i.m.)abolished the analgesic effect of T1-11 on acid-induced muscle painmodel, which further demonstrates the involvement of A3 adenosinereceptors in I_(T1-11). However, A3 adenosine receptor agonist (IB-MECA,1 nmole i.m.) did not have analgesic effect on acid-induced muscle pain.Instead, A2A adenosine receptor agonist (CGS21680, 1 nmole i.m.) showedpartial analgesic effect on the acid-induced muscle pain (FIG. 4).Accordingly, CGS21680 in high dose (10 μM) induces an outward current inA2A^(−/−) muscle afferent DRG neurons, indicating CGS21680 is a partialagonist for the I_(T1-11).

The involvement of NK1 receptor in I_(T1-11) was further determinedbecause NK1 receptor antagonist RP67580 (10 μM, n=17) inhibitedI_(T1-11). Like I_(SP-O), I_(T1-11) is resistant to GTP dialysis andmediated via M-type potassium channel. T1-11 enhanced M current involtage shift from −50 mV to −20 mV in muscle afferent neuronsexpressing I_(SP-O). These results indicated that T1-11 enhanced M-typepotassium currents through the NK1-associated receptors in aG-protein-independent manner. A3 adenosine receptors were proven to beinvolved in the NK1-associated receptor complex.

Therapeutic Effect of T1-11 on Fibromyalgia

It was further shown that T1-11 was an excellent therapeutic compound intwo mouse models of fibromyalgia. The first model was the acid-inducedchronic muscle pain model, in which mice developed chronic muscle afterintramuscular acid injection and a genistein treatment (see FIG. 8).T1-11 showed a dose-dependent analgesic effect on mice that havedeveloped the chronic muscle pain wherein the doses of T1-11 were in therange of 75-150 μg/kg (i.p.).

The second fibromyalgia model is developed by Ueda's group, in whichmice were treated with intermittent cold stress for 2 days (Nishiyori &Ueda, 2008). Mice treated with intermittent cold stress will developlong-lasting (>2 weeks) mechanical and thermal hyperalgesia. Analgesiceffect of T1-11 was tested in these mice 5 day after intermittent coldstress (ICS). We found that T1-11 in 30 μg/kg (i.p.) was the therapeuticdose to treat the pain (see FIG. 9). Moreover, we found T1-11 andsubstance P have synergistic effect in treating the ICS-induced pain.T1-11 in 3 μg/kg or SM-substance P in 0.6 mg/kg (a selective agonist forNK1 receptor) alone did not show analgesic effect on the ICS-treatedmice. However, combined T1-11 in 3 μg/kg with 0.6 mg/kg SM-substance Pshowed analgesic effect on the ICS-treated mice.

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1. A method of treating pain, comprising administering to a subject inneed thereof a therapeutically effective amount of an adenosine analogthat activates NK1 receptor signaling, thereby inducing outward current.2. The method of claim 1, wherein the pain is acid-induced pain.
 3. Themethod of claim 2, wherein the pain is acid-induced muscle pain.
 4. Themethod of claim 3, wherein the pain is acid-induced chronic muscle pain.5. The method of claim 1, wherein the pain is selected from the groupconsisting of inflammatory pain, cancer pain, chest pain, back pain,facial pain, joint pain, muscular pain syndromes, neuropathic pain,peripheral pain, cancer and tumor pain, sympathetic pain, postoperativepain, and post-traumatic pain.
 6. The method of claim 1, wherein thepain is fibromyalgia, myofascial pain, bladder pain syndrome or paincasued by irritable bowel syndrome.
 7. The method of claim 1, whereinthe adenosine analog is isolated from a Gastrodia extract.
 8. The methodof claim 1, wherein the adenosine analog is a compound of Formula (I):

or a pharmaceutically acceptable salt thereof, wherein: X is O, S orCH₂; R¹ is selected from the group consisting of NHR⁴, NH(CH₂)_(n)R⁴,NH—NHR⁴, NHCONHR⁴, NH—OR⁴, O—NHR⁴, and SR⁴; R² is selected from thegroup consisting of hydrogen (H), halogen, cyano, OR⁴, NHR⁴, substitutedor unsubstituted alkyl, substituted or unsubstituted alkenyl,substituted or unsubstituted alkynyl, substituted or unsubstitutedcycloalkyl, substituted or unsubstituted aryl (Ar), substituted orunsubstituted aralkyl, and a substituted or unsubstituted heterocyclyl;R³ is selected from the group consisting of halomethyl, hydroxymethyl(HOCH₂), alkoxymethyl (R⁴OCH₂), azidomethyl (N₃CH₂), aminomethyl(H₂NCH₂), substituted or unsubstituted aminomethyl, amidomethyl(H₂NCOCH₂), sulfanylmethyl (R⁴S), sulfonylmethyl (R⁴SO₂),triazolylmethyl, cyanomethyl (N≡CCH₂), cyano, substituted orunsubstituted carbonyl (R⁴CO), COOH, COOR⁴, substituted or unsubstitutedaminocarbonyl (R⁴HNCO), substituted or unsubstituted alkynyl, andsubstituted or unsubstituted tetrazole; n is 1,2 or 3; each instance ofR⁴ is independently selected from the group consisting of H, substitutedor unsubstituted alkyl, cycloalkyl, substituted or unsubstituted Ar,substituted or unsubstituted aralkyl, and a substituted or unsubstitutedheterocyclyl; Ar is selected from the group consisting of substituted orunsubstituted phenyl, substituted or unsubstituted polyarene, and asubstituted or unsubstituted heterocycle.
 9. The method of claim 8,wherein the adenosine analog is a compound of Formula (II):

or a pharmaceutically acceptable salt thereof.
 10. The method of claim9, wherein the adenosine analog is N⁶-(4-hydroxybenzyl)adenosine havingthe formula T1-11:

or a pharmaceutically acceptable salt thereof.
 11. The method of claim9, wherein the adenosine analog is N⁶-(4-hydroxybenzyl)adenosine havingthe formula JMF 1998:

or a pharmaceutically acceptable salt thereof.
 12. The method of claim9, wherein the adenosine analog is a compound having the formulaJMF2665:

or a pharmaceutically acceptable salt thereof.
 13. The method of claim8, wherein the adenosine analog is a compound of Formula (III):

or a pharmaceutically acceptable salt thereof, wherein Het is anoptionally substituted heterocycle of 5- or 6-membered ring or fusedring containing at least one nitrogen, oxygen or sulfur heteroatoms. 14.The method of claim 13, wherein Het is selected from the groupconsisting of pyrrole, furan, thiophene, pyridine, piperidine,piperazine, indole, benzofuran, benzothiophene, and quinoline.
 15. Themethod of claim 14, wherein the adenosine analog is a compound havingthe formula JMF 1907:

or a pharmaceutically acceptable salt thereof.
 16. The method of claim8, wherein the adenosine analog is a compound of Formula (IV):

or a pharmaceutically acceptable salt thereof.
 17. The method of claim16, wherein the adenosine analog is a compound having the formulaCGS21680:

or a pharmaceutically acceptable salt thereof
 18. The method of claim 1,wherein the adenosine analog is selected from the group consisting ofT1-11, JMF1907, JMF1998, JMF2665, and CGS21680.
 19. (canceled)
 20. Themethod of claim 1, wherein the adenosine analog is administered incombination with a further active agent for treating pain, wherein thefurther active agent is different from the adenosine analog. 21-26.(canceled)